1. Field of the Invention
The present invention relates to an interface apparatus for communication terminal equipment units, and more particularly to an interface apparatus which selectively connects one of a plurality of communication terminal equipment units with one telephone line.
2. Description of the Prior Art
Telephone sets have been used as communication terminal equipment units, along with facsimile apparatuses, image drawing communication terminal units, no-ringing communication terminal unit (hereinafter referred to as "telephone type terminal equipment") and data terminal equipment unit such as personal computers.
The circuit shown in FIG. 5 is a known connecting means for a connecting data terminal equipment (abbreviated to "DTE") unit with a telephone line. In FIG. 5, reference numeral 1 designates an exchange, 3C designates a telephone set, 5D designates a DTE unit, 7 designates a switch box, 22 designates a network control unit (NCU), 25 designates a modulator/demodulator equipment (MODEM) and l.sub.4 designates a telephone line.
As will be understandable from the drawing, the DTE unit 50 is connected with the telephone line by using the switch box 7. Here, the switch box 7 is connected with the telephone line l.sub.4, the telephone set 3C and the DTE unit 5D. By manual operation of the switch box 7, the line l.sub.4 is connected with the telephone set 3C or the DTE unit 5D.
This connection is, however, carried out manually, so that it is very difficult to promptly respond to the switch-over (exchange) between communication with the telephone set and with the DTE unit.
A control apparatus as shown in FIG. 6 has been proposed for solving this problem. The control apparatus comprises a switch box 7, an NCU 22, a MODEM 25 and a port T5 connected to a DTE unit 5D. The NCU 22 controls the switch box 7 to automatically connect the line l.sub.4 with the telephone set 3C or with the DTE unit 5D.
One control apparatus as shown in FIG. 6 must be installed for each telephone line. In other words, for a plurality of the DTE units the same number of telephone lines is required.